A basic task to which the present invention is directed is the application of discrete lengths of tapes, films, foils or the like to larger articles, such as container blanks, envelopes, continuous webs or the like at specific locations on such articles. In order to do this most effectively and efficiently, it is desired to apply the discrete lengths of web material to articles as they are moved continuously, while maximizing the speed at which the articles are moved relative to the applying system. Moreover, the discrete lengths should come from a strip of web material that is provided from a continuous supply such as a roll and is severed into the discrete lengths of web material to be continuously transferred to the articles for precise placement thereon.
As is well known, vacuum wheels can be used as a part of a cutting system, as the transfer means for moving discrete lengths of web material from a cutting point to an application point, and for applying the discrete length of web material to a continuously moving article passed thereby. Typically, such vacuum wheels include a plurality of evenly spaced anvils located on the periphery of the vacuum wheel which cooperate with a like number of knives or an integral fraction thereof also evenly spaced about the periphery of an adjacent cutting wheel. The vacuum wheel and cutting wheel are relatively rotated and timed with respect to one another such that the knives sequentially engage the anvils at a cutting point of the apparatus. A continuous length of web material is fed to the peripheral surface of the vacuum wheel prior to the cutting point at a set feed rate, while the vacuum wheel is rotated at an angular velocity providing a faster surface speed of its outer peripheral surface than the feed rate of the web material supply. Then, at the cutting point the continuous length of web material is severed into discrete lengths each time a knife of the cutting wheel is brought into cooperating contact with an anvil of the vacuum wheel. Thereafter, each discrete length of web material is moved at the speed of the vacuum wheel to an application point at which the discrete length of web material is applied to the article as it is moved tangentially to the vacuum wheel by a continuous conveying means.
Examples of machines in accordance with the above described in U.S. Pat. Nos. 2,291,841 to Staude, 2,723,604 to Fischer, 2,990,081 to De Neui et al., and 3,750,511 to Toensing. The Staude and Fischer patents are specifically directed to the application of patches or windows cut from a supply of web material to articles such as envelopes. De Neui et al. and Toensing, however, are directed to the application of discrete lengths of adhesive tape to the surfaces of articles generally. Although the Staude invention is directed to a transfer wheel that is not a vacuum wheel, it instead uses one or more positively driven belts to hold the cut patches against the transfer wheel between the cutting point and the application point.
In order to position the discrete lengths of web material, whether made from film to be a patch or window or from an adhesive type, onto the articles moved beneath the application point at a specific location on each article, prior art machines generally rely on guiding systems for bringing the contiuous strip of web material to the vacuum wheel and the appropriate timing of the cutting wheel, vacuum wheel, and the conveying means for moving the articles continuously. Such guide means normally include at least one drive roll for advancing the strip of web material at the aforementioned set feed rate to the vacuum wheel. The guide means typcially also includes one or more guide rollers which generally laterally align the strip of web material onto the circumferential surface of the vacuum wheel. Furthermore, the set feed rate at which the strip of web material is supplied determines the length of each discrete length of web material to be applied to the article.
These machines are satisfactory for positioning patches, windows of pieces of tape to articles at specific locations on the articles that do not require precise alignment; however, such machines are unsatisfactory in situations where very precise positioning of a discrete length of web material is required on the article passed through the machine. In other words, although these prior art machines do bring the patches, windows or tape pieces to a specific general location on the article passed through the machine, they are inadequate when it is necessary to very precisely position a discrete length of web material at an exact location on the articles moved through the machine.
One particular problem lies in the lateral alignment of the strip of web material on the peripheral surface of the vacuum wheel. As above, heretofore this has been accomplished be relying on a guide roller or series of such rollers from which the strip is advanced to the vacuum wheel. Such, however, does not prevent the strip from wandering from side to side as it engages with the surface of the vacuum wheel. In one known method for assisting the lateral alignment, a fixed flange has been provided around a peripheral edge of the vacuum wheel against which an edge of the strip of web material rides. The problem with the provision of such a flange is that the flange must extend along the periphery of the circumferential surface around the entire vacuum wheel which thus becomes an obstruction at the point of application of the vacuum wheel to the articles conveyed thereby. Thus, such a vacuum wheel could not be used in the most common instances because the presence of the flange at the application point of the vacuum wheel to the articles would reduce the applying pressure from the vacuum wheel or would damage the article. Moreover, such a flanged vacuum wheel is limited by its design to machines having a moving applicator pad upon which the articles are supported at the application point, either radially or axially moving, so that the edges of the articles are moved out of the way of the flange during application. Such machines are disadvantageous in that they are more expensive and complex and typically require cam action to move the applicator pad either axially or radially. Such cam actions experience greater wear problems requiring more maintenance and increasing costs and down time.
Another problem of such vacuum wheel applicators and guide systems happens as a result of the feeding the web material to the vacuum wheel at a slower speed than the surface speed of the vacuum wheel and the cutting of the web material while both the web material and the vacuum wheel are moving. That is, it is difficult to cleanly sever a discrete length of the web material from the strip as it is being fed continuously at a slower rate than the surface rates of both the vacuum wheel and the cutting wheel. There is a tendency for stretching or tearing of the strip during the cutting operation. A well known manner utilized by the prior art for overcoming this problem is to increase the feed rate of the strip to the surface rate of the vacuum wheel during the instance that the strip of web material is cut. To do this, a loop forming roll or wobbler roller is provided on a pivotally mounted arm which is cyclically driven so as to reciprocably move the wobbler roller up and down to increase and decrease the size of the strip loop formed by the roller and to change the feed rate of the strip of web material as compared to the surface rate of the vacuum wheel. More particularly, the pivot arm is driven in one direction to decrease the loop size and thereby momentarily increase the feed rate of the strip of web material to the surface rate of the vacuum wheel so that cutting of the strip of web material occurs at that instant. Then, the pivot arm is driven in the reverse direction to reform or increase the size of the loop in the strip for slowing or even momentarily reversing the strip feed rate once again. Such operation occurs on a cyclic basis and can be appropriately timed with respect to the cyclic operation of the cutting wheel and vacuum wheel so that the strip is brought to the speed of the vacuum wheel at each instance of cutting.
However, even with the provision of a loop forming or wobbler roller for increasing the strip speed to the vacuum wheel speed during cutting, such systems have been found to be unsatisfactory when accurate placement of the discrete lengths of web material are to be applied. In this regard, it has been discovered that inertia experienced by the loop forming or wobbler roller as the roller reverses its rotational direction effects the length of the discrete lengths of web material to be cut. Specifically when the roller is reversed in rotational direction as compared to the rotational direction of feed, the roller pulls the strip of web material slightly back from the vacuum wheel. Thus, the next cut discrete length may be slightly shorter in length, and the next may be too long, and so on. The result is an inconsistency of the discrete lengths of web material applied to the articles. Moreover, the inconsistent discrete lengths of web material affect the longitudinal alignment of the discrete lengths of the web material with respect to the articles. None of the prior art recognizes or addresses this problem.
One particular application which requires the very accurate lateral and longitudinal positioning of a discrete length of web material to an article is the application of a strip or fillet of stiffening material coated with a layer of adhesive to a scored blank of a paperboard gable-top container. The combination of such a strip of stiffening material to a gable-top container blank are disclosed in the following U.S. patents to Wyberg which are commonly owned by the assignee of the present invention: U.S. Pat. No. 4,712,727 issued Dec. 15, 1987; U.S. Pat. No. 4,756,426 issued Jul. 12, 1988; U.S. Pat. No. 4,762,234 issued Aug. 9, 1988; U.S. Pat. No. 4,792,048 issued Dec. 20, 1988; U.S. Pat. No. 4,813,547 issued Mar. 21, 1989; 4,813,548 issued Mar. 21, 1989; U.S. Pat. No. 4,869,372 issued Sep. 26, 1989; U.S. Pat. No. 4,869,373 issued Sep. 26, 1989 and U.S. Pat. No. 4,872,562 issued Oct. 10, 1989. The strip is provided as a part of an easy opening feature for gable-top containers and must be accurately aligned with regard to the fold lines and edges of the container blanks in order to work effectively. If the strip is not properly aligned, the container may not fold properly or the easy opening feature may be rendered ineffective. Moreover, it is important to not only precisely align the strip on the blank, it is desired to do so with a maximum of efficiency such that the alignment does not hinder the speeds obtainable by vacuum wheel systems.